Mastering SOLID Principles

Explore the single responsibility principle (SRP) as a core of solid design. See how separating concerns keeps classes focused on one reason to change, improving maintainability and testability.

Identify multiple responsibilities in a class and apply SRP to separate user input handling, data validation, email sending, and database saving, then refactor the user class accordingly.

Apply SRP by refactoring a user class into three responsibilities: user data, email service, and user repository for database interactions, making code more maintainable and less prone to side effects.

Identify common pitfalls when applying the single responsibility principle (SRP) in large codebases, like over segmentation, misidentifying responsibilities, and sacrificing SRP for speed; learn strategies to apply SRP effectively.

Apply the single responsibility principle to refactor a real-world e-commerce module into dedicated classes—order validator, order calculator, repository, and customer notifier—making the system more modular and easier to test.

Revisit the single responsibility principle and its impact on readability, testability, and maintainability. Identify responsibilities, refactor code to SRP, and apply it in Python to avoid pitfalls and improve quality.

Open-closed principle guides refactoring a simple discount calculator into modular types, percentage, fixed amount, and seasonal, improving extensibility and maintainability without altering existing code.

Explore how the open-closed principle guides real-world software, using a payment processing system to add new methods without changing existing code, ensuring modularity and scalability.

Identify common open closed principle traps like overengineering and unnecessary abstractions, which create fragile code; learn why quick fixes by modifying existing classes can snowball into larger issues.

Refactor a logging framework to adhere to the open-closed principle, turning a violating design into a robust, extensible solution that supports console, file, and remote outputs.

Recap the open-closed principle and its aim to keep systems open for extension but closed for modification, reinforcing stable, adaptable code through real-world examples.

The Liskov substitution principle states that a superclass can be replaced by its subclass without changing program correctness, enabling reusability, maintainability, and polymorphism.

Explore the Liskov substitution principle with a square versus rectangle analogy, showing how violating behavioral contracts disrupts area calculations and how abstract shapes enforce correct substitution.

Show how overriding a fly method in penguin breaks the Liskov substitution principle, causing unexpected behavior. Refactor by separating flying and non-flying birds to ensure subclasses uphold base contracts.

Explore strategies to avoid LSP violations by applying design by contract, including preconditions, postconditions, and invariants, and strengthen LSP compliance through unit testing and inheritance hierarchy tests.

Master the Liskov substitution principle by ensuring subclasses replace their parent classes without changing behavior, using design by contract, thorough testing, and real-world case studies to build robust, scalable code.

Learn how the interface segregation principle—isp—in Python prevents bloated interfaces by creating client-focused interfaces, reducing the impact of changes and keeping code flexible and maintainable.

Identify common violations of the interface segregation principle (ISP) when a class implements an interface with unused methods, causing empty method syndrome; learn avoidance through code examples in subsequent lectures.

Refactor the interface segregation principle (isp) by splitting a fat interface into smaller ones—worker, eater, and sleeper—to show robot implements only work and human implements work, eat, and sleep.

Explore the real-world application of ISP by designing smaller, purpose-built interfaces for API clients, yielding modular, maintainable, and scalable code.

Refactor the printer code to apply the interface segregation principle by creating three specific interfaces for printing, scanning, and faxing; basic printer prints, advanced handles all features.

Explore the interface segregation principle, creating small client-specific interfaces to reduce complexity and boost maintainability, and prepare for the dependency inversion principle.

Demonstrates how the dependency inversion principle guides refactoring data preprocessing to depend on a data loader interface, enabling runtime selection of CSV, database, or API loaders via dependency injection.

Apply the dependency inversion principle by introducing a notifier interface and decoupling the notification service from concrete notifiers like email, SMS, and push.

Recap the dependency inversion principle and the value of abstractions over concrete implementations for maintainable code, and note how the five SOLID principles underpin scalable software in Python and beyond.

Apply all five SOLID principles to a real-world e-commerce project, showing how user management, product catalog, order processing, and notifications contribute to a well-structured, maintainable, and scalable application.

Apply the single responsibility principle by separating user management, authentication, and profile services. Adopt open-closed, Liskov substitution, interface segregation, and dependency inversion across the product catalog, order processing, and notifications.